The present invention relates to an automatic door closer which includes a closer shaft, projecting from a housing, to which the door to be closed is connected for turning movement therewith, and which is biased by spring means to a position in which the door is closed. The door closer includes further a link member connected to the closer shaft so as to change its position in accordance with the turning of the latter, onto which a support member acts, which can be held in an active position to thereby counteract the turning moment imparted to the closer shaft by the spring means, and which can electromagnetically released to an inactive position so that the closer shaft may turn under the influence of the spring means again to the close position. In automatic door closers of the aforementioned kind, the support member, cooperating with the link, holds thus the door in open position against the force of the spring means tending to move the door to the closed position. An automatic door closer of the aforementioned kind is known by the German Gebrauchsmuster No. 7,403,756. The link member in this known construction is constructed by an annular flange which can be clamped onto the closure shaft, which flange is provided at its outer periphery with a plurality of circumferentially spaced cutouts in which the support members can respectively engage. The support member is electromagnetically held in the engaged position in order to hold the door in selected open positions. The member may move out of the respective cutouts when the electromagnet is deenergized so that the door may move to the closed position under the influence of the turning moment imparted to the closer shaft. It is also known in such constructions to spring-bias the support member into a respective cutout aligned therewith, but all these arrangements have the disadvantage that the door can be held open only in a plurality of turned positions angularly spaced from each other and, of course, these positions have to be selected in such a manner that the support member will move, under the influence of the spring means connected thereto, into the respective cutout, which will require a careful and slow movement of the door to one of the selected positions in which the door should be held open.
The German Offenlegungsschrift No. 2,201,594 discloses further an automatic door closer in which damping means, including cylinder and piston means for limiting the speed at which the door can be closed, are provided with an electromagnetically operable valve which in its closed position prevents fluid from flowing out from the working compartment of the cylinder and piston means to this stop the closing movement of the door until the electromagnet is deenergized so that the valve will move to its open position.
From the German Offenlegungsschrift No. 2,311,343 it is further known to connect to the movable element of damping means, limiting the speed of turning of the door and constructed as cylinder and piston means, an additional cylinder and piston arrangement which, in turn, by means of a valve, which can be electromagnetically held in a closed position, permits to maintain the door of an automatic door closer in any desired open position until the electromagnet is deenergized.
Automatic door closers of the aforementioned kind, which include damping means and electromagnetically operated control means connected thereto, are, however, expensive to manufacture and require a relatively large space.